WASHINGTON – Utility crews struggled to catch up with a backlog of millions of people without electricity for a fourth hot day Tuesday as frustration grew and authorities feared the toll of 24 storm deaths could rise because of stifling conditions and generator fumes.

Power was back for more than a million customers but lights – and air-conditioning – were still out for about 1.26 million homes and businesses in seven states and the District of Columbia. The damage was done by powerful wind storms that swept from the Midwest to the Mid-Atlantic late Friday, toppling trees and branches into power lines and knocking out big transmission towers and electrical substations.

Utilities were warning that many neighborhoods could remain in the dark for much of the week, if not beyond. Public officials and residents were growing impatient.